1. Field of the Invention
This invention relates generally to patterned-media magnetic recording disks, wherein each data bit is stored in a magnetically isolated data island on the disk, and more particularly to a patterned-media disk and disk drive with patterned nondata servo fields for head-positioning.
2. Description of the Related Art
Magnetic recording hard disk drives with patterned magnetic recording media have been proposed to increase the data density. In patterned media, the magnetic recording layer on the disk is patterned into small isolated data islands such that there is a single magnetic domain in each island or “bit”. The single magnetic domains can be a single grain or consist of a few strongly coupled grains that switch magnetic states in concert as a single magnetic volume. This is in contrast to conventional continuous media wherein a single “bit” may have multiple magnetic domains separated by domain walls. To produce the required magnetic isolation of the patterned islands, the magnetic moment of the spaces between the islands must be destroyed or substantially reduced so as to render these spaces essentially nonmagnetic. Alternatively, the patterned media may be fabricated so that that there is no magnetic material in the spaces between the islands. U.S. Pat. Nos. 5,820,769; 5,587,223; and 6,383,598 are representative of various types of patterned media and their methods of fabrication.
Like conventional non-patterned or continuous-media disks, patterned-media disks also have nondata servo regions that are used for read/write head positioning. The nondata servo regions in patterned-media disks contain servo blocks or islands separated by nonmagnetic spaces. The servo blocks form a servo pattern that generates a servo readback signal that is demodulated into a position error signal (PES) for positioning the read/write head to the desired data track and maintaining it on track. The proposed method for formatting this type of disk is to DC “erase” the disk during manufacturing with a large magnet, leaving all of the servo islands magnetized in the same direction. Thus for a patterned-media perpendicular magnetic recording disk, all of the servo islands would have a magnetization direction either “into” or “out of” the surface of the disk. However, because only a single polarity of magnetization is used with this method, half of the available signal amplitude from the servo islands is sacrificed and thus the signal-to-noise ratio (SNR) is less than optimum. Pending application Ser. No. 11/148,918, published as US2006/0280975 A1 and assigned to the same assignee as this application, describes a magnetic recording disk with discrete servo islands having alternating polarity in the along-the-track direction and patterned into four separate fields so as to form a conventional amplitude-type quadrature servo pattern. The amplitudes of the readback servo signal in the four fields are demodulated to generate the PES.
What is needed is a patterned-media magnetic recording disk with nondata servo islands that have alternating polarity of magnetization to provide optimal SNR, but also form an improved amplitude-type servo pattern that is relatively easy to demodulate into a PES.